Method for legalizing mixed-cell height standard cells of IC

A method for legalizing mixed-cell height standard cells of an IC is provided. A target standard cell is obtained in a window of a global placement. The target standard cell has a first area overlapping a first standard cell located in a first row of the window, and a second area overlapping a second standard cell located in a second row of the window. The target standard cell and the first standard cell are moved until the target standard cell does not overlap the first standard cell in the first row of the window. The target standard cell and the first standard cell are clustered as a first cluster when the target standard cell does not overlap the first standard cell. The first cluster is moved away from the second standard cell in the second row until the second standard cell does not overlap the first cluster.